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No I am not trolling. Unfortunately I don't have a garage or underground parking and as such the car is exposed to the elements in winter. Recently to my bafflement I have had ice buildup all over the inside of the car's front window.

My first instinct is to take the ice scraper (which I use for ice buildup on the outside of same front window of my car), to it, however I have become more apprehensive when discussing this with a friend who thought it could scratch the glass.

What are best practices for my situation and are there ways to prevent this (parking in a garage or underground parking somewhere to prevent the car from being exposed to the elements is not an option).

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  • You're much more likely to scratch the outside than the inside, because the're more chance of grit on the outside. If you use a brass scraper (I've seen them in Germany) you might want to be careful of the corners, that's all.
    – Chris H
    Dec 12, 2016 at 12:20

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First: how to fix.

You can take a scraper to the inside of the car window. The windows are definitely hardy enough to withstand having a scraper used on it. I do it all the time, and have never had a problem. However, if you are concerned about it, there is an easy work-around: heat up your car for a few minutes and turn on the heat full blast pointed at the window. A few minutes should suffice to clear it up plenty to make it totally safe to drive.

Second: how to prevent.

To get to the reason behind it, you have to understand what is going on. Basically, the window is cooling down from the outside-in, and the water in the warm humid air on the inside of your car is condensing on your window. There are several possible solutions. One is to leave all the windows in your car a crack open. I do not recommend this if the car can get snow on it.

Another solution is to leave the car on for a few minutes after you stop and everyone hops out with the heat on full blast and the de-frost enabled. This will send a good blast of dry air into the passenger compartment and should keep your car from frosting up on the inside.

TBH, at this point in the winter, I have the heat on high enough that the dry air from of the engine is enough to counteract the humid air that I and my passengers are breathing out.

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  • Rubber car mats might help as well. I've certainly had my share of frost inside the windshield, and one thing seems consistent for me - the cloth floor mats are damp with melted snow. Eventually it freezes, but not before it humidifies the air.
    – Lathejockey81
    Dec 10, 2016 at 14:04
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    When I had a car prone to icing up inside, I'd finish the journey with full heat, full blow, and the driver's window ajar, then quickly cover the windscreen when I stopped. This made a huge difference, though the other windows ended up worse. Scapring the inside often doesn't work very well unless you use a fiddly,small scraper because of the curvature
    – Chris H
    Dec 12, 2016 at 12:18
  • Random thought, but I would love to have this clarified: Would it likely make any significant difference if the windows are at least slightly open while running the defroster? (I figure the moist air needs to go somewhere, and providing an easy escape for it would seem like it can't really hurt.) I have been battling the same issue recently with the weather being humid and quickly changing between above freezing and below freezing, but I could easily leave the car running for a few minutes after parking. Just wondering which option w.r.t. windows would be most likely to be effective.
    – user
    Jan 8, 2017 at 14:47
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When you park at work, try to orient your car towards the south, which will help solar heating of the front of the car. With any luck your ice will sublimate, and when you run the heater in the car the fresh but dry air will further get moisture out of the inside compartment.

Outside, polymer coatings such as Rain-X on glass, and wax on painted surfaces will help.

If your windshield is glass, a normal plastic ice scraper will not scratch the glass.

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You can prevent frost on the inside of the windshield in 2 ways.

  1. use a blanket.
  2. Make sure the air inside the car is not moist enough to condense into an ice layer. Frost inside the car is unusual, so you may have a leak somewhere, with rainwater coming into the car (check under your carpets). Find the leak, dry out the car (a long drive with the heat on full blast, and/or use a dehumidifier).
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Running the A/C (with the heat on full) will help to reduce humidity in the car, which in turn will reduce the amount of frost on the inside. This works because chilling the air reduces its ability to hold moisture and causes the water vapor in the air to condense out. If you do this for a few minutes before parking, it will help prevent frost on the inside. If you do it when there is frost, the reduced humidity in the air will speed the evaporation of the frost.

If you have access to power where you park the car a block heater will both make life easier on the engine and it will also give you heat sooner after start up. I put one in each of our cars and on frosty mornings notice that the area above the defroster vents is almost always clear – I have them on a timer and it takes about an hour or two to get the engine up to operating temperature when the temperature is around freezing.

For scraping the inside of the windshield, I find that a driver's license or credit card works very well. I almost always have one or the other with me :-) and they flex nicely to follow the contours of the windshield.

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  • If you live in a country that uses chip-based credit cards, it's best to scrape your windows with one that has already expired! (This may not be an issue in the USA, though.)
    – alephzero
    Dec 10, 2016 at 7:31
  • Aw, come on, another 20 or 30 years and we'll be mostly switched over to the (obsolete by then) chip based cards :-) But not to worry, we'll still be measuring them in inches.
    – dlu
    Dec 10, 2016 at 7:34

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